1. Field of the Invention
The present invention relates a coder, and more particularly, to a mechanical coder.
2. Description of the Prior Art
Referring to FIG. 1, which depicts a conventional obstructing type coder including an emitter 10, a receiver 20 and an optical shutter 30. The optical shutter 30 is made of opaque material. A plurality of rectangular openings 31 are formed on the periphery of the optical shutter 30. While the optical shutter 30 is rotating, the light emitted by the emitter 10 may pass through the openings 31 or be interdicted by the opaque optical shutter 30. As the light emitted from the emitter 10 passes through the openings 31, the receiver 20 accepts an "ON" signal. Conversely, as the light emitted from the emitter 10 is interdicted by the opaque optical shutter 30, the receiver 20 receives an "OFF" signal. Thus, a plurality of "ON" signals and a plurality of "OFF" signals constitute a continuous light-and-shade signal having constant interval. The light-and-shade signal is received and then transferred into a digital logic signal for output.
In order to increase the resolution, increasing the number of the shutter 32 is desired. However, the more the numbers of shutters 32, the more serious is the problem caused by scattering and diffraction. Scattering and diffraction will result in the difficulty in clarifying "ON" signal or "OFF" signal. Thus the receiver 20 to judge the received signal exactly. Hence it is difficult to increase the resolution without limits.
Referring to FIG. 2, which depicts another conventional guidance type coder including an emitter 10, a receiver 20 and an optical shutter 30 made of transparent material. There are a plurality of gear-shaped projections 33 and a plurality of recesses 34 formed on the periphery of the optical shutter 30. Additionally, there are a plurality of refraction planes 35 formed on the inner portion of the optical shutter 30. While the optical shutter 30 is rotating, the light emitted by the emitter 10 may be refracted to projections 33 or recesses 34. As the light emitted by the emitter 10 is refracted to projections 33, the receiver 20 accepts an "ON" signal. Conversely, as the light emitted by the emitter 10 is refracted to recesses 34, the receiver 20 receives an "OFF" signal. Thus, a plurality of "ON" signals and a plurality of "OFF" signal constitute a continuous light-and-shade signal having a constant interval. The light-and-shade signal is received and then transferred into a digital logic signal for output.
The resolution of the guidance type coder is higher than that of the above-mentioned obstructing-type coder. However, the optical distance of the guidance type coder is longer than that of above-mentioned obstructing type coder because that the light is indirectly guided to the receiver 20. Moreover, before the receiver 20 the refracted light, the light has grown weaker already. In order to prevent the light guided to the receiver 20 from being attenuated, the intensity of the emitter 10 must be increased. More power consumption is needed and the lifetime of emitter 10 is shortened.
Referring to FIG. 3, a traditional mechanical coder is depicted. The traditional mechanical coder consists of a signal-separating wheel 40, a common terminal 54, a first terminal 52 and a second terminal 53. Additionally, there are a first conductive portion 41, a plurality of second conductive portions 42, a plurality of third conductive portions 43 and an insulating portion 43 formed on a main surface of the signal-separating wheel 40 having a disk-shaped outline. It is worth noting that there are several ladders formed of one second conductive portion 42 and one third conductive portion 43. That is, for the first terminal 52 and the second terminal 53, each of second conductive portions 42 and each of third conductive portions 43 are not on the same level. However, the common terminal 54, the first terminal 52 and the second terminal 53 are placed on the same level and coupled to the main surface of the signal-separating wheel 40. While the signal-separating wheel 40 is rotating, the first terminal 52 and the second terminal 53, placed on the same level, continuously receive the "ON" signal or the "OFF" signal, respectively. The "ON" signal and the "OFF" signal constitute a digital logic signal.
The advantages of the traditional mechanical coder include lower power consumption, non-scattering, non-diffraction and longer lifetime. The traditional mechanical coder is generally employed in the wireless device, notebook or the device requiring lower power consumption. However, the disadvantages of the traditional mechanical coder are identified as follows.
(1) The signal-separating wheel is made from a general PCB (printed circuit board). Then the signal-separating wheel is etched or stamped. Thus the thickness of the first conductive portion, the second conductive portion and the third conductive portion may be slightly different from that of the insulating portion. That is, there is an altitude formed between the conductive portion and the insulating portion. This will result in bounce of the terminal, which leads to unstable signal and errors in receiving the signal.
(2) Because the signal-separating wheel is etched or stamped, there are many sharp teeth formed on the boundary of the conductive portion and the insulating portion. This will cause an unstable signal and errors in receiving the signal.
(3) The required precision is high and the extra work is difficult to do, so the yield is low.
(4) The common terminal, the first terminal and the second terminal are placed on the same level, and they are coupled to the main surface of the signal-separating wheel, so they suppress the rotation of the signal-separating wheel.